To develop new purging regimens for ABMT the ability to predict potential for purging of tumor cells from BM is important. Since the sensitivity of human B cell lymphoma to hyperthermia is not known, we examined its effect on the growth of B cell lymphoma cell lines (Raji and Daudi) in vitro to evaluate potential for purging clonogenic tumor cells from normal marrow by heat, using a limiting dilution assay to measure log depletion of tumor cells in a 20-fold excess of normal BM. When exposed to heat (42-43 degrees C) for 120 min, both clonogenic Raji and Daudi cells were dramatically reduced (a 4-to-6 log reduction) with time, whereas at 42 degrees C over half and at 43 degrees C 10% of normal granulocyte-macrophage progenitor cells survived for the same time period. This high level of lymphoma cell depletion by heat correlated with that of immunologic and pharmacologic studies. In addition, these survival curves during heating were found to correlate with the Gompertz-Makeham formula--a law of human mortality. This formula may be useful in predicting the purging effect of heat. These results suggest that in vitro hyperthermia could be applied effectively for the elimination of residual, clonogenic lymphoma cells in autologous marrow grafts before ABMT.